Researchers at Princeton University have created the world's purest samples of gallium arsenide (GaAs), a semiconductor whose uses range from solar cells to cell phone circuits. Their work to explore quantum phenomena in low magnetic fields involves physics without a "established theoretical framework" and is of great significance to the understanding of electrons in this field.
The first authors of the paper, Kevin Villegas Rosales and Edwin Chung, both received PhDs in electrical and computer engineering (ECE) from Princeton this year. ECE professor Mansour Shayegan and senior research scholar Loren Pfeiffer are the main researchers.
In an email to the Princeton Daily, Sayagen emphasized the importance of this achievement.
“New samples/materials only have about 1 out of every 10 billion impurities, which means there is only one unwanted atom (impurity) out of every 10 billion wanted atoms,” he wrote. "It's like there is only one bad guy on the earth!"
This level of purity developed using molecular beam epitaxy (a method of depositing individual crystals in layers) exceeds that of silicon samples used to determine the one kilogram standard. The GaAs chip is about the same size as a pencil eraser, and researchers use it to probe the properties of electrons.
Sayergen wrote: "I have always been fascinated by the electronic phenomena and phases that appear in very'clean' systems, in which there are very few impurities and defects."
To understand these interactions, the team connected the sample and frozen it to a temperature lower than that found in space, then surrounded it with a strong magnetic field and applied a voltage. While lowering the magnetic field, they discovered an effect without a traditional theoretical basis.
The first effect involves Wigner crystals. In this phenomenon, the gaseous state is selected to form a lattice structure to minimize the influence of mutual repulsion.
Historically, physicists believed that Wigner crystals needed a strong magnetic field, which Villegas Rosales described as a magnetic field that was large enough to "float a frog." However, the researchers found that this kind of crystallization is also possible in a much weaker field.
This effect is closely related to the purity of the GaAs sample.
"Electron crystals can only be formed when the host material (gallium arsenide in our case) is very pure, otherwise impurities will interfere with the crystal and randomize the position of the electrons," Shayegan added.
In addition, the researchers studied the fractional quantum Hall effect originally discovered by ECE professor Daniel Tsui within a given framework. They found that their system has a larger "activation gap."
The significance of the research of Villegas Rosales and Zhong still goes beyond theory.
"In a more general sense, the new sample may be used for topological quantum computing, or it may be used as a better (faster) dedicated transistor," Shayegan explained. "The electrons in high-purity samples can travel a long distance, about 1 mm, before they hit the impurities and deviate from the orbit. This kind of'ballistic' movement of the electrons is desirable in fast transistors."
These findings were published in the journal "Nature Materials". This work was conceived by Chung and Pfeiffer, and Pfeiffer also designed and built a molecular beam epitaxy chamber. Other co-authors mentioned in the paper include Kirk W. Baldwin, Pranav Madathil, and KW West, all of whom are affiliated with the electrical engineering department of the university.
After completing his PhD, Vilegas Rosales is now working in a quantum computing startup, while Chung stayed in these two laboratories as a postdoctoral researcher.
Villegas Rosales and Chung did not respond to requests for comment.
Tara Agarwal is a news writer for The Prince. You can contact her at ta3150@princeton.edu.
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